Technical Field
The present disclosure generally relates to additive manufacturing, and more particularly, to powder delivery systems and methods used in additive manufacturing apparatus.
Description of the Related Art
Traditionally, materials are processed into desired shapes and assemblies through a combination of rough fabrication techniques (e.g., casting, rolling, forging, extrusion, and stamping) and finish fabrication techniques (e.g., machining, welding, soldering, polishing). Producing a complex assembly in final, usable form (“net shape”), which often may require not only forming the part with the desired materials in the proper shapes but also providing the part with the desired combination of metallurgical properties (e.g., various heat treatments, work hardening, complex microstructure), typically requires considerable investment in time, tools, and effort.
One or more of the rough and finish processes may be performed using manufacturing centers, such as Computer Numerically Controlled (CNC) machine tools. CNC machine tools use precisely programmed commands to automate the manufacturing process. The commands may be generated using computer-aided design (CAD) and/or computer-aided manufacturing (CAM) programs. Examples of CNC machines include, but are not limited to, mills, lathes, mill-turns, plasma cutters, electric discharge machines (EDM), and water jet cutters. CNC machining centers have been developed which provide a single machine having multiple tool types that is capable of performing multiple different machining processes. Such machining centers may generally include one or more tool retainers, such as spindle retainers and turret retainers holding one or more tools, and a workpiece retainer, such as a pair of chucks. The workpiece retainer may be stationary or move (in translation and/or rotation) while a tool is brought into contact with the workpiece, thereby performing a subtractive manufacturing process during which material is removed from the workpiece.
Because of cost, expense, complexity, and other factors, additive manufacturing techniques have been developed that would replace all or part of the conventional subtractive manufacturing steps. In contrast to subtractive manufacturing processes, which focus on precise removal of material from a workpiece, additive manufacturing processes add material, typically in a computer-controlled environment, by creating successive layers of material to form a three-dimensional object. Additive manufacturing techniques may improve efficiency and reduce waste while expanding manufacturing capabilities, such as by permitting seamless construction of complex configurations which, when using conventional manufacturing techniques, would have to be assembled from a plurality of component parts. For the purposes of this specification and the appended claims, the term ‘plurality’ consistently is taken to mean “two or more.” The opportunity for additive techniques to replace subtractive processes depends on several factors, such as the range of materials available for use in the additive processes, the size and surface finish that can be achieved using additive techniques, and the rate at which material can be added. Additive processes may advantageously be capable of fabricating complex precision net-shape components ready for use. In some cases, however, the additive process may generate “near-net shape” products that require some degree of finishing.
Additive manufacturing techniques include, but are not limited to, powder bed fusion processes such as laser sintering, laser melting, and electron beam melting; direct energy deposition processes such as laser engineered net shaping direct metal/material deposition, and laser cladding; material extrusion such as fused deposition modeling; material jetting including continuous or drop-on-demand; binder jetting; vat polymerization; and sheet lamination including ultrasonic additive manufacturing. In some direct energy deposition processes, powder is injected from one or more nozzles into a focused beam of a laser to melt a small pool of the substrate material. Powder contacting the pool will melt to generate a deposit on the substrate.
Material deposition systems used in additive manufacturing devices typically use open-loop control to provide a constant powder flow rate to the nozzle. This approach can introduce inconsistencies in deposition track morphology when the steady state is disturbed, such as acceleration or deceleration of the velocity of relative movement between the deposition head and the substrate. More recently, material deposition systems have been proposed that use a feedback system that may adjust the rate at which powder is delivered. Conventional powder delivery systems, however, may be slow to adjust to the change in powder demand, thereby slowing the additive manufacturing process and/or introducing inconsistencies in the deposited additive material.